The Menshutkin Reaction in the Gas Phase and in Aqueous Solution: A Valence Bond Study

Su, Peifeng; Ying, Fuming; Wu, Wei; Hiberty, Philippe C.; Shaik, Sason

doi:10.1002/cphc.200700626

Cited by 38 publications

(69 citation statements)

References 59 publications

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“…Examination of the configuration weight of structure 5 in the VBSCF ground state indicates that it has the smallest contributions both in the reactant and product structures and the largest component at the transition state (Figure 1). 10 This trend is consistent with and can be related to the partial charge on the central carbon as noted previously by Song et al in their study of the identity S N 2 reactions involving halogen ions 9,10. In fact, there are many different ways of representing the partition of structure 5 into the two diabatic states, which means that there are also many different ways of defining effective diabatic states.…”

Section: Effective Two-state Valence Bond Modelsupporting

confidence: 87%

On the Construction of Diabatic and Adiabatic Potential Energy Surfaces Based on Ab Initio Valence Bond Theory

2008

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A theoretical model is presented for deriving effective diabatic states based on ab initio self-consistent field valence bond (VBSCF) theory by reducing the multi-configurational VB Hamiltonian into an effective two-state model. We describe two computational approaches for the optimization of the effective diabatic configurations, resulting in two ways of interpreting such effective diabatic states. In the variational diabatic configuration (VDC) method, the energies of the individual diabatic states are variationally minimized. In the consistent diabatic configuration (CDC) method, both the configuration coefficients and orbital coefficients are simultaneously optimized to minimize the adiabatic ground-state energy in VBSCF calculations. In addition, we describe a mixed molecular orbital and valence bond (MOVB) approach to construct the CDC diabatic and adiabatic states for a chemical reaction, whereas the VDC-MOVB method has been described previously. Employing the symmetric SN2 reaction between NH3 and CH3NH3+ as a test system, we found that the results from ab initio VBSCF and from MOVB calculations are in good agreement, suggesting that the computationally efficient MOVB method is a reasonable model for VB simulations of condensed phase reactions. The results indicate that CDC and VDC diabatic states converge, respectively, to covalent and ionic states as the molecular geometries are distorted from the minimum of the respective diabatic state along the reaction coordinate. Furthermore, the resonance energy that stabilizes the energy of crossing between the two diabatic states, resulting in the transition state of the adiabatic ground-state reaction, has a strong dependence on the overlap integral between the two diabatic states and is a function of both the exchange integral and the total diabatic ground-state energy.

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Section: Effective Two-state Valence Bond Modelsupporting

confidence: 87%

On the Construction of Diabatic and Adiabatic Potential Energy Surfaces Based on Ab Initio Valence Bond Theory

2008

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“…Although this perspective has been quantitatively illustrated only with gas-phase diabatic states, most of the considerations are equally valid for condensed-phase reactions, for which a number of valence-bond electronic structure approaches are now available 61,63,65,67,68,72,101,141. In previous work on aqueous S N 2 reactions, the MOVB method based on VDC diabatic states led to solute-solvent interaction energies that vary weakly with the reaction coordinate, in contrast to previous studies of other S N 2 reactions using the EVB method 94.…”

Section: Discussionmentioning

confidence: 99%

“…The use of valence-bond (VB) theory to study these reactions quantitatively is less common because of the higher computational cost and slow convergence (with respect to adding configurations) of VB calculations, but VB theory has the advantage of providing unique insight into the electronic structure 54–59. Examples of nucleophilic substitution reactions studied using VB methodology include the identity X − + RX′ → XR + X′ − reactions (R = alkyl; X, X′ = F, Cl, Br, I);54–57,60–68 nonidentity versions of these reactions (X not the same as X′);54–57 the Cl − + CH 3 SH 2 + → ClCH 3 + SH 2 and H 3 N + CH 3 SH 2 + → H 3 NCH 3 + + SH 2 reactions;61 the particular case CH 3 Cl + NH 3 →Cl − + CH 3 NH 3 + of the general Menshutkin reaction;55,58,69–72 reactions of esters and ketyl radical anions;56,73 reactions at peptide bonds;74 and reaction at phosphorus 75…”

Section: Introductionmentioning

confidence: 99%

Perspective on Diabatic Models of Chemical Reactivity as Illustrated by the Gas-Phase S_N2 Reaction of Acetate Ion with 1,2-Dichloroethane

Valero

Song

Gao

et al. 2008

J. Chem. Theory Comput.

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Diabatic models are widely employed for studying chemical reactivity in condensed phases and enzymes, but there has been little discussion of the pros and cons of various diabatic representations for this purpose. Here we discuss and contrast six different schemes for computing diabatic potentials for a charge rearrangement reaction. They include (i) the variational diabatic configurations (VDC) constructed by variationally optimizing individual valence bond structures and (ii) the consistent diabatic configurations (CDC) obtained by variationally optimizing the ground-state adiabatic energy, both in the nonorthogonal molecular orbital valence bond (MOVB) method, along with the orthogonalized (iii) VDC-MOVB and (iv) CDC-MOVB models. In addition, we consider (v) the fourfold way (based on diabatic molecular orbitals and configuration uniformity), and (vi) empirical valence bond (EVB) theory. To make the considerations concrete, we calculate diabatic electronic states and diabatic potential energies along the reaction path that connects the reactant and the product ion-molecule complexes of the gas-phase bimolecular nucleophilic substitution (SN2) reaction of 1,2-dichloethane (DCE) with acetate ion, which is a model reaction corresponding to the reaction catalyzed by haloalkane dehalogenase. We utilize ab initio block-localized molecular orbital theory to construct the MOVB diabatic states and ab initio multi-configuration quasidegenerate perturbation theory to construct the fourfold-way diabatic states; the latter are calculated at reaction path geometries obtained with the M06-2X density functional. The EVB diabatic states are computed with parameters taken from the literature. The MOVB and fourfold-way adiabatic and diabatic potential energy profiles along the reaction path are in qualitative but not quantitative agreement with each other. In order to validate that these wave-function-based diabatic states are qualitatively correct, we show that the reaction energy and barrier for the adiabatic ground state, obtained with these methods, agree reasonably well with the results of high-level calculations using the composite G3SX and G3SX(MP3) methods and the BMC-CCSD multi-coefficient correlation method. However, a comparison of the EVB gas-phase adiabatic ground-state reaction path with those obtained from MOVB and with the fourfold way reveals that the EVB reaction path geometries show a systematic shift towards the products region, and that the EVB lowest-energy path has a much lower barrier. The free energies of solvation and activation energy in water reported from dynamical calculations based on EVB also imply a low activation barrier in the gas phase. In addition, calculations of the free energy of solvation using the recently proposed SM8 continuum solvation model with CM4M partial atomic charges lead to an activation barrier in reasonable agreement with experiment only when the geometries and the gas-phase barrier are those obtained from electronic structure calculations, i.e., methods i–v. These comparis...

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“…[15][16][17] This strategy for activation is becoming more common in part because the bis(trifluoromethanesulfonyl)imide (TFSI) anion is an attractive component in certain types of ionic liquids. The S N 2 reaction is itself much better studied than nucleofugality as a general concept; theoretical studies exist for both ionic and Menshutkin-type S N 2 reactions, including solvent effects, 21,22 S N 2 reactions at neutral nitrogen, 23,24 comparisons of front side vs. back side S N 2, 25,26 studies employing valence bond methods, 27 analyses of Marcus theory using S N 2 as a model, 28 and analyses of the influences of periodicity on the anionic S N 2 reaction. TFSI is generally considered to be a poorly associating ion; it is also thought to plasticize polymeric lithium ion conductors, leading to a lower glass transition temperature in the polymer, and hence better conductivity than other anions of similar lithium ion affinities.…”

Section: Introductionmentioning

confidence: 99%

Nucleofugality in oxygen and nitrogen derived pseudohalides in Menshutkin reactions: the importance of the intrinsic barrier

Spahlinger

Jackson

2014

Phys. Chem. Chem. Phys.

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In order to study the nucleofugality of polyatomic anionic leaving groups derived from oxygen and nitrogen, a contingent of 19 methylating agents consisting of amines or alcohols activated with carbonyl or sulfonyl substituents has been examined via ab initio calculations. We have calculated gas phase activation energies for alkylation of ammonia, and methyl cation affinities. We find that polyatomic anionic leaving groups derived from nitrogen will have higher activation energies for Menshutkin (SN2) alkylation even when they have similar methyl cation affinities. This inherent deficit in the nucleofugality of nitrogen-derived leaving groups appears to be a result of the way bond cleavage is synchronized with bond formation to the incoming ammonia nucleophile. The nitrogen leaving groups showed greater dissociation from the methyl fragment than oxygen leaving groups relative to the length of the forming carbon-nitrogen bond. Additionally the second sulfonyl group present in a sulfonimide appears to be less effective at activating nitrogen due to a preference for tetrahedral geometries at the departing nitrogen in the transition states involving leaving sulfonamide groups. Optimal delocalization of electron density is therefore frustrated due to the geometry of the leaving group.

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The Menshutkin Reaction in the Gas Phase and in Aqueous Solution: A Valence Bond Study

Cited by 38 publications

References 59 publications

On the Construction of Diabatic and Adiabatic Potential Energy Surfaces Based on Ab Initio Valence Bond Theory

On the Construction of Diabatic and Adiabatic Potential Energy Surfaces Based on Ab Initio Valence Bond Theory

Perspective on Diabatic Models of Chemical Reactivity as Illustrated by the Gas-Phase S_N2 Reaction of Acetate Ion with 1,2-Dichloroethane

Nucleofugality in oxygen and nitrogen derived pseudohalides in Menshutkin reactions: the importance of the intrinsic barrier

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The Menshutkin Reaction in the Gas Phase and in Aqueous Solution: A Valence Bond Study

Cited by 38 publications

References 59 publications

On the Construction of Diabatic and Adiabatic Potential Energy Surfaces Based on Ab Initio Valence Bond Theory

On the Construction of Diabatic and Adiabatic Potential Energy Surfaces Based on Ab Initio Valence Bond Theory

Perspective on Diabatic Models of Chemical Reactivity as Illustrated by the Gas-Phase SN2 Reaction of Acetate Ion with 1,2-Dichloroethane

Nucleofugality in oxygen and nitrogen derived pseudohalides in Menshutkin reactions: the importance of the intrinsic barrier

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Perspective on Diabatic Models of Chemical Reactivity as Illustrated by the Gas-Phase S_N2 Reaction of Acetate Ion with 1,2-Dichloroethane